CN1322176C - Having gamma-LiAlO2Method for preparing single crystal film covering layer substrate - Google Patents

Abstract

A method for _preparing a substrate with a γ- _LiAlO2 single-crystal thin film covering layer, the steps of which are: first synthesize and prepare a γ- _LiAlO2 target material, _and then use radio frequency magnetron Gamma-LiAlO ₂ single crystal thin film is prepared on the substrate, the process of the method of the invention is simple and easy to operate, and the substrate material with the gamma-LiAlO ₂ single crystal thin film covering layer is suitable for epitaxial growth of high-quality GaN.

Description

Preparation Method of Substrate with γ-LiAlO2 Single Crystal Thin Film Covering Layer

technical field

The invention relates to the epitaxial growth of InN-GaN-based blue-light semiconductors, in particular to a method for preparing a substrate with a gamma- _LiAlO2 single-crystal thin film covering layer by radio frequency magnetron sputtering.

Background technique

Wide bandgap III-V compound semiconductor materials represented by GaN are attracting more and more attention, they have excellent characteristics, such as stable physical and chemical properties, high thermal conductivity and high electron saturation velocity, direct bandgap materials The optical transition probability is an order of magnitude higher than that of the indirect bandgap, so wide bandgap InN-GaN-based semiconductors are used in blue and green light-emitting diodes (LEDs) and laser diodes (LDs), high-density information reading and writing, underwater communications, It has broad application prospects in deep water exploration, laser printing, biological and medical engineering, as well as ultra-high-speed microelectronic devices and ultra-high-frequency microwave devices. Due to the relatively high melting point of InN-GaN and the high saturated vapor pressure of N ₂ , it is very difficult to prepare InN-GaN bulk single crystals, so InN-GaN is generally grown on heterogeneous substrates by epitaxial technology.

Due to GaN's high melting point, high hardness, and high saturated vapor pressure, high temperature and high pressure are required to grow large-sized GaN bulk single crystals. The Polish High Pressure Research Center only produced strips with a width of 5 mm at a high temperature of 1600 ° C and a high pressure of 20 kbar. GaN bulk single crystal. At present, the technology to grow large-sized GaN bulk single crystal is still immature, and the cost of growth is high, and there is still a long distance from practical application.

Sapphire crystal (α-Al ₂ O ₃ ) and silicon are easy to prepare, cheap, and have good high temperature stability. α-Al ₂ O ₃ is currently the most commonly used InN-GaN-based epitaxial substrate material (see Jpn. J. Appl. Phys., Vol. 36, 1997, p. 1568).

Lithium aluminate (γ-LiAlO ₂ ) is an InN-GaN-based epitaxial substrate material that has only received attention in recent years. Because of its very small lattice mismatch with GaN epitaxial film, only 1.4%, it is expected to become A rather ideal GaN epitaxial substrate material, see USP6218280B1, Kryliouk Olga, Anderson Tim, Chai Bruce, "Method and apparatus for producing group-III nitrides".

Significant disadvantages of the aforementioned prior art substrates (α-Al ₂ O ₃ , silicon or γ-LiAlO ₂ ) are:

(1) Using α-Al ₂ O ₃ and silicon as the substrate, the lattice mismatch between the substrate and GaN is high, up to 14%, so that the prepared GaN film has a high dislocation density and a large number of point defect;

(2) Due to the non-stoichiometric volatilization of LiAlO ₂ melt at high temperature, crystal growth is difficult, and it is difficult to obtain large-size, high-quality LiAlO ₂ single crystals. The largest sapphire diameter reaches 350mm, while the diameter of LiAlO ₂ is less than 100mm ; Moreover, the processing of the substrate will cause a lot of waste of raw materials.

Contents of the invention

The technical problem to be solved in the present invention is to overcome the above-mentioned shortcoming of the prior art, provide a kind of preparation method that is used as InN-GaN base blue light semiconductor epitaxial growth with γ-LiAlO ₂ single crystal film covering layer substrate, the technology of this method Simple and easy to operate, the prepared substrate material is suitable for epitaxial growth of high-quality GaN.

The key point of the present invention is to use radio frequency magnetron sputtering method to directly press and generate γ-LiAlO ₂ covering layer on α-Al ₂ O ₃ or silicon substrate. Here α-Al ₂ O ₃ or silicon plays the role of supporting the thin layer of γ-LiAlO ₂ on it, and this kind of structure substrate is suitable for the epitaxial growth of high-quality GaN thin film.

The method of the invention includes two steps: firstly, preparation of γ-LiAlO ₂ , and then preparing a γ-LiAlO ₂ covering layer on α-Al ₂ O ₃ or a silicon substrate by radio frequency magnetron sputtering.

The present invention has γ-LiAlO ₂ The specific process flow of the preparation method of the single crystal thin film cover layer substrate is as follows:

<1> Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 600°C for 1.5 hours (above) to fully react to obtain γ- LiAlO ₂ , and then γ-LiAlO ₂ powder is pressed into the target material.

<2> γ-LiAlO ₂ thin films were prepared on single crystal substrates by radio frequency magnetron sputtering.

The mechanism of radio frequency magnetron sputtering is that Ar ⁺ becomes high-energy incident particles after being accelerated by an electric field and hits the γ- _LiAlO2 target material, collides with the target atoms, and transfers part of the momentum to the target atoms, and the target atoms collide with other target atoms to form A cascading process in which some target atoms near the surface gain sufficient momentum to move outward, are sputtered out of the target, and attach to a single crystal substrate placed a few centimeters from the surface of the target , Stacking, thus depositing γ-LiAlO ₂ film.

The features of the present invention are:

<1>, directly use γ-LiAlO ₂ as the target material and use radio frequency magnetron sputtering technology to generate γ-LiAlO ₂ covering layer on the single crystal substrate, avoiding the reaction with the substrate to prepare γ-LiAlO ₂ thin film, which has It is beneficial to control the thickness of the γ-LiAlO ₂ film and the uniformity of the film.

<2>, in the structure with γ-LiAlO ₂ film covering substrate, α-Al ₂ O ₃ or silicon only plays the role of supporting the γ-LiAlO ₂ thin layer on it, and a variety of substrates can be selected for support γ-LiAlO ₂ .

Detailed ways

The present invention will be further described below by specific examples.

The radio frequency magnetron sputtering technology preparation of the present invention has gamma-LiAlO The _concrete technological process of substrate of thin film is as follows:

<1> Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 600°C for 1.5 hours (above) to fully react to obtain γ- LiAlO ₂ , and then γ-LiAlO ₂ powder is pressed into the target material.

<2> The γ-LiAlO ₂ thin film was prepared on a single crystal substrate with a radio frequency magnetron sputtering device.

Example 1

Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere, and keep the temperature at 600°C for 1.5 hours (above) to fully react to obtain γ -LiAlO ₂ , and then press γ-LiAlO ₂ powder into a target;

Send the polished and cleaned α-Al ₂ O ₃ single crystal substrate into Edwards ESM100 radio frequency magnetron sputtering device. The size of the vacuum chamber of the device is φ322×270mm, and the vacuum system is mechanical pump, oil diffusion pump , with an additional liquid nitrogen cooling trap, the vacuum degree can reach 2×10 ^-4 Pa, the inner diameter of the target seat is 100mm, the cooling water is passed through the inner cavity, and the target is fixed with pressure rings and screws. The substrate base is φ250mm, and the cooling water is passed inside, and the distance between the target and the substrate is about 60mm. The RF power generator used for sputtering is controlled by transistors, the power can be adjusted in the range of 0-1000W, the output impedance is 50Ω, and the frequency is 13.56MHz. When depositing thin films by sputtering, the basic vacuum pressure of the instrument system is 2×10 ^-3 Pa, the RF power range is 100-250W, the target diameter is 85mm, the thickness is 3mm, and the sputtering working gas is high-purity argon with a purity ≥ 99.999%. Argon pressure is 6.6×10 ^-2 Pa, the substrate is a double-sided polished α-Al ₂ O ₃ single wafer, the substrate temperature is 600°C, and the film deposition rate is 0.063nm/s (38 Å/ min), the deposition rate is monitored by a quartz crystal oscillator, and the film thickness is 500nm.

Example 2

Weigh a certain amount of LiOH and Al ₂ O ₃ (molar ratio 2:1) into a reaction vessel, heat in an air atmosphere and keep the temperature at 600°C for a full reaction for 1.5 hours (above), to obtain γ-LiAlO ₂ , Then the γ- _LiAlO2 powder is pressed into the target material;

Put the polished and cleaned Si single crystal substrate into the Edwards ESM100 radio frequency magnetron sputtering device, the vacuum degree is greater than 2×10 ^-4 Pa, and the high purity argon gas with a purity ≥ 99.999% is used for sputtering, and the argon pressure is 6.6×10 ^-2 Pa, the substrate temperature is 700°C, the film deposition rate is about 0.063nm/s, and the film thickness is 500nm.

Experiments have proved that the process of this method is simple and easy to operate, and the prepared substrate material with γ-LiAlO ₂ single crystal thin film covering layer is suitable for epitaxial growth of high-quality GaN.

Claims (2)

1. A method for preparing a substrate with a γ- _{LiAlO2 single} -crystal film covering layer, which is characterized in that the γ- _LiAlO2 target is prepared first, and then the α- _Al2O3 or silicon substrate is deposited by radio frequency magnetron sputtering. A γ-LiAlO ₂ single crystal thin film covering layer is formed on the bottom. 2. The method for preparing a substrate with a γ- _LiAlO2 single crystal thin film covering layer according to claim 1, characterized in that it comprises the following specific steps: <1>Preparation of γ-LiAlO ₂ target material: Weigh a certain amount of LiOH and Al ₂ O ₃ in a molar ratio of 2:1, put them into a reaction vessel, heat in an air atmosphere, at 600°C, and hold for ≥1.5 hours. To fully react to obtain γ-LiAlO ₂ , and then press γ-LiAlO ₂ powder into a target; <2> Preparation of γ-LiAlO ₂ thin film on α-Al ₂ O ₃ or silicon single crystal substrate: Send the polished and cleaned α-Al ₂ O ₃ or silicon single crystal substrate into the radio frequency magnetron sputtering device , the basic vacuum pressure of the instrument system is 2×10 ^-3 Pa, the sputtering working gas is high-purity argon with a purity ≥ 99.999%, the substrate is a double-sided polished α-Al ₂ O ₃ or silicon single wafer, and the film deposition The deposition rate was 0.063nm/s, and the deposition rate was monitored by a quartz crystal oscillator, and the substrate material of the γ-LiAlO ₂ single crystal thin film covering layer was obtained.